Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $160.50   9.534%   $175.8021   $175.80   $175.80   $175.80  
  Purchase #2 $16.36   7.774%   $17.6318   $17.63   $17.65   $17.60  
  Purchase #3 $70.67   3.779%   $73.3406   $73.34   $73.35   $73.30  
  Purchase #4 $183.87   5.259%   $193.5397   $193.54   $193.55   $193.50  
  Purchase #5 $119.41   12.683%   $134.5548   $134.55   $134.55   $134.60  
  Purchase #6 $129.45   7.829%   $139.5846   $139.58   $139.60   $139.60  
  Purchase #7 $246.87   5.749%   $261.0626   $261.06   $261.05   $261.10  
  7 purchase totals = $927.13       $995.5162   $995.50   $995.55   $995.50